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For example, consider the following topology: AS1 AS2 AS3 ------------------------------- -------------------------- ---------------------------- Src PE -- P -- P – ASBR – ASBR – P – P – ASBR – ASBR – P – P – dst PE If the test message is send from Src PE to dst PE without the enhanced processing or the new TLV, the packet could traverse the network shown into AS3. If it encounters an error between the ASBR in AS3 and the first P router – say the packet is for an invalid FEC error case. In this case, the first P router would examine the packet and need to send a reply to the Src PE. However, if the Src PE is using an address for a network that is not distributed outside of AS1 (which might belong to a different provider than the addresses used in AS3), then the reply will never be forwarded back to Src PE. |